If aircraft are in emergency situations, several emergency measures are provided e.g. Emergency Locator Transmitters notifying rescue personal of a location of the aircraft or flight recorders that record flight and aircraft parameters to determine a cause of the emergency situation later on. Some of these emergency measures such as the flight recorder operate continuously whereas others such as the Emergency Locator Transmitters need to be activated. Emergency Locator Transmitters are nowadays equipped with acceleration sensors that activate the Emergency Locator Transmitter if high negative accelerations are sensed. The acceleration sensors essentially activate the emergency measure in the same moment an actual crash or impact occurs as the negative acceleration is a result of the impact. However, there have been occurrences of malfunctioning acceleration sensor based Emergency Locator Transmitters.
It appears that the transmitters were destroyed by the impact before the sensors detected that the aircraft experienced an impact or before the transmitters were able to establish a communications link and send an emergency signal. Hence, there is a need for a sufficiently early triggering, i.e. pre-crash or pre-impact, of emergency measures such as Emergency Locator Transmitters.
Such pre-crash or pre-impact triggering is, for example, also required for initiating the transmission of flight recordings from the aircraft to a ground control in case of an emergency. These transmitted flight recordings facilitate a rapid accident investigation without having to search for the flight recorders and avoid high costs during regular flight caused by continuous transmissions of flight recordings.
A different problem arises with another emergency measure in form of Deployable Flight Recorders. Deployable Flight Recorders are equipped with sensors that trigger an ejection or deployment of the Deployable Flight Recorder. Here, the problem is not a late deployment of the Deployable Flight Recorders but rather unintended deployments due to malfunction of the sensors. An unintentionally ejected flight recorder might cause damage to the aircraft and, in particular, cause damage to wherever it drops onto the ground. Thus, there also is a need to prevent an unintended triggering of emergency measures such as Deployable Flight Recorders.